1. Field of the Invention
The present invention relates to a rotary shaft device arranged in a main spindle of a machine tool and the like and rotatably supporting a rotary shaft including reciprocating flow passages for fluid.
2. Description of the Related Art
In a main spindle for a machine tool for example, reciprocating flow passages for fluid are arranged inside a rotary shaft for the purpose of cooling, and it is configured to supply the reciprocating flow passages with fluid through a rotary joint. With regard to the rotary joint, as described in JP-A-S51-100323, a structure is known in which a plurality of annular oil passage grooves are formed concentrically between end faces of a pair of disks facing with each other. Further, O-rings are provided between the adjacent annular oil passage grooves, and passage openings connected to each annular oil passage groove are opened in the outer end surface of the each disk to allow the fluid to be supplied.
However, the rotary joint described in JP-A-S51-100323 is of a one-way structure in which the fluid passes from one disk to the other disk. Therefore, it is difficult to apply the known structure to a rotary shaft provided with reciprocating flow passages inside thereof such as a main spindle of a machine tool. In particular, when the rotary shaft provided with the reciprocating flow passages rotates at a high speed, the fluid pressure increases inside the joint on the discharge side because of the pressure caused by the difference in the radius of a forward passage and a backward passage. As a result, the internal pressure of the rotary joint increases, which may lead to fluid leaking. On the other hand, the drastic drop of the fluid pressure inside the forward passage or inside the joint may cause an occurrence of cavitation.
Under such circumstances, the object of the present invention is to provide a rotary shaft device capable of inhibiting an occurrence of leakage and supplying fluid stably even if a rotary shaft provided with reciprocating flow passages for fluid rotates at a high speed.
In order to achieve the object, a first aspect of the present invention is a rotary shaft device including a rotary joint having a front joint disk and a rear joint disk. The front joint disk is arranged in a rear end face of a rotary shaft, which is provided with reciprocating flow passages. The rear joint disk is arranged so as to oppose the front joint disk and capable of being pressed against the front joint disk by a pressing part at a predetermined pressure. The front joint disk and the rear joint disk are provided with forward communication holes connected to a forward passages side of the reciprocating flow passages, and backward communication holes connected to a backward passages side of the reciprocating flow passages respectively.
Further, either the front joint disk or the rear joint disk opposing with each other has a ring-shaped inner seal projecting and abutting upon the opponent face on the axis side of the joint disk in the pressing state by the pressing part. Either the front joint disk or the rear joint disk opposing with each other also has a ring-shaped outer seal projecting, positioned concentrically with the inner seal, and abutting upon the opponent face on the outer periphery side of the joint disk in the pressing state by the pressing part.
A ring-shaped inner space and a ring-shaped outer space are adjacently arranged concentrically with each other between the inner seal and the outer seal. The ring-shaped inner space communicates with the forward communication holes or the backward communication holes. The ring-shaped outer space also communicates with the forward communication holes or the backward communication holes. The forward and the backward communication holes at least in the front joint disk are arranged at an equal distance in the peripheral direction of the opposing face.
A second aspect of the present invention is the rotary shaft device according to the first aspect in which a ring-shaped middle seal separates the inner space and the outer space, and being projectingly arranged concentrically with the inner seal and the outer seal at least in either of the faces opposing with each other.
A third aspect of the present invention is the rotary shaft device according to the second aspect in which the middle seal is arranged to project less than the inner seal and the outer seal so as to form a gap through which the inner space and the outer space communicate with each other in the pressing state.
A fourth aspect of the present invention is the rotary shaft device according to the third aspect in which the gap is variable according to the number of revolution of the rotary shaft.
A fifth aspect of the present invention is the rotary shaft device according to any of the preceding aspects in which the front joint disk is provided with a throttle mechanism reducing a flow passage cross-sectional area of the backward communication holes on the far side of the rotation center of the rotary shaft as the number of revolution of the rotary shaft increases.
A sixth aspect of the present invention is the rotary shaft device according to the fifth aspect in which the throttle mechanism is formed of a slide body and an energizing part. The slide body crosses the backward communication hole, and being slidable in the radial direction of the front joint disk. The energizing part energizes the slide body in the slide direction increasing the flow passage cross-sectional area.
A seventh aspect of the present invention is the rotary shaft device according to the first aspect in which the inner space and the outer space are formed so as to be united.
A eighth aspect of the present invention is the rotary shaft device according to the first aspect in which the rear end of at least either of the forward communication holes and the backward communication holes arranged in the front joint disk are arranged lower than a radial position of the reciprocating flow passages connected in the radial direction of the rotary shaft.
According to the first aspect of the present invention, the rotation balance is improved. Therefore, leakage hardly occurs because of arranging adjacently even if the rotary shaft provided with the reciprocating passages rotates at a high speed.
According to the second aspect of the present invention, leakage of fluid can be prevented more effectively in addition to the effect of the first aspect of the present invention.
According to the third aspect of the present invention, sealing resistance can be reduced even if the middle seal is provided. Further, an increase in the pressure of the outer space caused by the centrifugal force can be suppressed in addition to the effect of the second aspect.
According to the fourth aspect of the present invention, the pressure drop of the inner space and the pressure rise of the outer space caused by the centrifugal force with an increase in the number of revolution can be improved gradually in addition to the effect of the third aspect.
According to the fifth aspect of the present invention, the fluid pressure drop and changes in the flow rate inside the rotary shaft can be suppressed by adoption of the throttle mechanism in addition to the effect of either of the first to fourth aspect.
According to the sixth aspect of the present invention, it is available to easily and reasonably obtain the throttle mechanism operated by the centrifugal force generated by rotation of the rotary shaft in addition to the effect of the fifth aspect.
According to the seventh aspect of the present invention, the flow rate of the fluid to the reciprocating flow passages of the rotary shaft is increased. When the fluid is the cooling liquid, the heat transfer coefficient is increased. Therefore, cooling efficiency can be improved in addition to the effect of the first aspect.
According to the eighth aspect of the present invention, the fluid can be supplied to the reciprocating passages stably without disturbing flow-in by cavitation, and leakage from the outer seal due to an increase in pressure at an outlet can be prevented in addition to the effect of the first aspect.